1. Field of the Invention
This invention relates to a thrust device for a mining machine cooperating with a sectional conveyor, in particular at the face below ground, e.g. for a roller coal cutter running on a string of trunking of a chain conveyor, wherein traverse of the coal cutter takes place by means of a pinion engaging with a rack located on the conveyor and preferably divided into equal longitudinal sections.
2. Description of the Prior Art
In such devices, power is usually supplied to the pinion by a drive located on the coal cutter. Rotation of the pinion is converted by means of the rack into a linear thrust which propels the coal cutter along the face. The sections of the conveyor, which preferably consist of a chain conveyor with a string of trunking and a chain drive located at one or both ends, often serve as a rail track for the cutter, absorbing the reaction forces of the thrust device.
On the one hand, the string of trunking must be able to yield in a horizontal and vertical direction at the joints between the trunking, so that the string is, in the event of geological disturbances, in a position to deflect in two planes at right angles to each other. For this reason, the majority of conveyors have a degree of play between their sections which, in the case of the trunking of chain conveyors, can, for example, amount to 15 mm. On the other hand, the thrust force transferred to the trunking leads to a displacement of the line of trunking, mainly in its longitudinal direction, the total displacement observed along the face, as a rule, amounting to several times the degree of play.
In a known design ("Gluckauf" 111, 1975, No. 18 863, FIG. 4), the rack is divided into longitudinal sections which are firmly connected together, but are fixed to the trunking in a manner permitting limited play in the longitudinal direction, by way of bolts and elongated holes. As the elongated holes, which determine the degree of play, can only be given a limited length, while the conveyor is made up of a plurality of sections of trunking whose individual play is multiplied at the end of the conveyor, a difficulty arises in that the conveyor is maintained practically rigid by the rack so that destructive thrust forces are applied to the longitudinal sections of the rack. If, however, the necessary length compensation of the individual conveyors were supplemented by a corresponding compensation for the sectional lengths of the rack, then there would occur pitch errors at the junction of the adjacent longitudinal sections which could adversely affect propulsion of the cutter. Because of this, the known design could not be utilised where trunking lines were installed with the normal play and/or geological disturbances with hollows and ridges were to be overcome.
It is also known (German Gebrauchsmuster No. 1,781,817) to employ a sprocket chain instead of a rack divided into longitudinal sections, which chain is fixed at both ends in a manner permitting limited yielding and is guided on the conveyor between the fixing points. However, the problem of length compensation can not be solved by this means either. On the other hand, in practice, thrust devices have proved themselves of use in which in place of the pinion a sprocket chain is used and, for the rack, drive shafts having movable cylindrical bolts ("Gluckauf", supra, 862). With these shafts also, meshing inaccuracies occur under the operational necessity of length compensation, which are apparently taken up by the play present in the chain. Chains of this kind are, however, relatively complicated and sensitive elements of machinery.